I successfully used an Esim on my recent Best of Spain Tour and wanted to share how I managed it. There are many possible variations.
I have an iPhone Xr on Verizon. The main line is still on the physical sim, and I didn't want to deal with moving it to the esim, or purchasing a Spanish Sim. All that I wanted was a data only package for the esim. There are several companies that offer the data only packages, Gigsky, Truphone, and Ubigi. Gigsky is pretty expensive, but Ubigi offers a 10Gb/30 day package for $19 for use in Spain only. I installed the Ubigi app and opened an account before leaving the US.
I did not want to trigger the Verizon Travelpass, but I wanted it to be available if needed. The Travelpass is triggered if you make or receive a call, or send a text. It is necessary to keep your primary phone number active if you want to send and receive iMessages. To avoid having the Travelpass triggered, I forwarded all calls to another number (I forwarded to a Google Voice number, but that is another topic), and I set my iMessages to not be able to "Send as SMS" to avoid an iMessage being converted to a regular text (I'm not really sure if this was necessary, but I took the precaution anyway).
The last thing that I did before shutting down the phone in the US was to turn off the Verizon data and turn on the Ubigi data. Once I got to Spain and turned the phone back on, the Ubigi data was able to connect to the Orange network, and I was able to purchase a plan through the Ubigi app.
The phone used the Orange network throughout the trip, and for the most part, I had a really good signal. I was able to iMessage, and use plenty of data. I only needed to make a couple of calls back home, and I was able to do that using Wifi calling from the hotel.
A couple of precautionary notes. While the phone connected to the Orange network really quickly, it took several hours for text messages to come through. If you are using text messages for authentication, you may not be able to do that immediately. Also, the Ubigi app demanded an update during my trip. Keep in mind that I had installed it a couple of weeks before the trip. I could not use the app during most of the trip to monitor cellular data usage, but I just looked under cellular data to see how much I had used. If I had wanted to purchase additional data, I would not have been able to do that without an update to the app. Any app that refuses to work without an update a few weeks after the install is a problem (in my opinion).
The service worked well for me, at a very reasonable price. Since this whole system is new, and it took me awhile to figure how to get it to work, I wanted to share this with others.